Large water storage – a solution

A windmill pumps water when the wind blows and that is not always when you need the water. At some point or the other you will have to make a decision about creating extra storage for the pumped water. Here are some notes from my experience that might offer you a lower cost option.

At the pointReturn location, the installed windmill is estimated to have a capacity to pump 20,000 litres per day [lpd]. This is an estimate based on the wind regime here. However, that is not an output you can be certain about. Obviously, the output also depends on the water available underground.

A windmill is an ideal solution in arid areas where water resources are poor or undeveloped as the pointReturn site is. For each revolution, a typical windmill pumps out a little more than a litre. It follows that it needs to be supplied at better than just that rate. An electric motor on the other hand, will pump hundreds of times the output of a windmill -provided the well has that quantity of water available. It is quite common to see monster pumps sucking wells dry in a short burst and running themselves to destruction, if left unattended. The pleasures of flicking a switch on are often visited upon by the pain of having failed to switch off in time.

Where inflow of water into the well is low, a windmill is a good solution. At pointReturn, the mill is at stand still for several hours in a day; it turns over lazily for some hours and runs at great speed for some. The output during these phases are obviously varied. There is an additional unpleasant wrinkle: in the dry months – as the last two months have been- the water arriving at the borewell is low and is sucked out quite quickly. So the sight of the mill turning at great speed might in fact mean no water pumped at all. But a windmill, for having run dry, isn’t ruined quite as quickly or badly as an electric pump is.

The short point is the water output from a windmill is unsteady. The indulgence -wasteful, I might add- of switching a motor on and seeing a violent gush of water issue forth, is not possible with a windmill. One needs to accumulate water as it is pumped out and use it discreetly when required.

It makes sense to store the water at a height so that it can flow by gravity to where needed, when needed. At pointReturn walter is stored atop the one sturdy structure there is – the strongRoom. This serves several purposes, primary among them is as a storage where we can lock away tools and basic essentials; the site is unmanned at nights.

The strongRoom is only 10’x10′; the area of its roof is therefore, limited. There sit four old plastic tanks I have had for about 11 years now; each is of a 1,000 litre capacity. They are made of Linear Low Density Polyethylene [LLDP]. Such tanks were popularised by the brand ‘Sintex’, a name that has become generic.

On good days, when the wind is blowing fairly and the borewell is fed by sturdy underground springs, following rains, the overhead tanks [OHT] have overflowed within hours. The 4,000 litres of storage capacity has just not been enough. It was a frequent sight on many mornings to see the overflow amount to a strong wasteful stream.

The solution was obvious but the costs were forbidding. What options did I have?

Build a large concrete OHT

Extend the strongRoom and place additional LLDP tanks on top

Build a series of elevated storages all over the site and have the overflow run to them

I first met Sreenivas Ghatty in 2003 in Bangalore. We were at a conference on tree based biodiesel. I actually sat in the section reserved for […]

Pointers

“...the most successful secessionist struggle ever waged in India - the secession of the middle and upper classes to a country of their own, somewhere in the stratosphere where they merge with the rest of the world's elite”:: Arundati Roy - 'Listening to the grasshoppers'